Portable radio communications require battery power. Because battery life is limited, efforts are on-going to provide longer lasting batteries and discover new techniques for minimizing battery drain. While one way of conserving power is to turn the radio off until the user wants to transmit a message, such a radio is of limited value because outside parties could not reach the user. As a result, portable radios typically monitor at least one communications channel in order to receive information/messages from outside sources that transmit on that channel. Unfortunately, if the receiver continuously monitors such a channel in order to detect and process those messages of interest to that radio user, current is continuously drawn, power is consumed and battery life is decreased. The useful life of the portable radio is therefore limited unless the user submits to the inconvenience of carrying additional batteries.
Radio systems that include digital communications capability, such as modern trunked radio and cellular systems, typically control and coordinate portable radio communications using a radio frequency channel designated (and often dedicated) as the control channel. Whenever radios are not actively engaged in a communication on a working channel via a working channel transceiver or repeater, they tune to a control channel frequency transmitted via a control channel transceiver/repeater under the control of a central controller or manager in charge of the geographical site or cell area in which the radio is located to detect and process digital control messages. Over this control channel, the radios transmit digital working channel request messages (e.g., when the user depresses a push-to-talk key) and status signalling, and the controller sends out working channel assignments including a transmit and receive frequency for the communication/call as well as other control signalling messages.
To ensure that radios always can confirm they are tuned to and monitoring the control channel, the central controller generates a continuous stream of digital control messages over the control channel. Consequently, radios within range of the control channel transceiver can always tune or retune to the control channel frequency, obtain the synchronization required for digital communications, and detect and process the received digital messages. Some of the control channel messages contain information the radio needs to process, and once processed, take perhaps some responsive action, e.g., a channel assignment. However, most of the traffic over the control channel are repeatedly transmitted messages, sometimes called "idle messages." One example of an idle message is the identification number or other code of the central controller which identifies the control channel, site or cell of the controller, etc.
For each received message irrespective of message type, the radio demodulates that message into binary ones and zeros and performs various data processing tasks on that demodulated message to determine the validity of the message, the type of the message, and its content. Each control channel message frame commonly includes plural copies of a message, each message copy having error correction bits included in an error correction field along with a substantive message field. Plural copies of the message in each message frame are used by the receiving radio to increase the probability of receiving a correct message. For example, one message processing operation to ensure the accuracy of the received data is to perform a voting operation of the copies of the received message in the message frame and to select as the substantive message bits and error correction bits for that message frame those bits found in the majority of the message copies, i.e., a majority vote. Subsequently, the error correction bits and the substantive message bits of the voted message are processed in accordance with some type of error detection and/or correction algorithm(s) such as conventional cyclic redundancy check algorithms (CRC). The radio microprocessor then typically decodes the message in some fashion to detect, for example, the type of message received, e.g., an idle message, a channel assignment message, etc.
Unfortunately, when the radio's microprocessor performs these majority vote and CRC type data processing operations for each message received on the control channel in accordance with program instructions stored in program memory, the microprocessor consumes considerable current. Each time the voting and CRC processes are performed on each received message, the microprocessor activates numerous registers, addresses and retrieves instructions from memory, and performs numerous arithmetic and manipulation operations. The power drain on the battery to support these operations is significant.
The inventor of the present invention recognized that radios can monitor and be in synchronization with the digital signalling over the control channel without having to continuously process and decode redundant, idle type messages to the degree described above. Portable radios in accordance with the present invention monitor various control messages and remain synchronized with a radio control channel. The radio fully processes and decodes one or more initially received messages to detect and maintain bit and word synchronization and to detect the message type. If the message is an idle message, the radio stores the idle message in memory. Rather than voting, CRC'ing, and decoding every received message, each subsequent message received on the control channel is compared with the stored message to determine if they match. If they do match, the radio enters a low power mode of operation where that message is ignored as a redundant idle message. By avoiding any further processing and decoding, the life of the radio battery is extended.
In other words, if the radio is receiving a series of redundant, idle messages identical to the idle message previously fully processed, decoded, and stored, the radio avoids further processing and decoding of these identical idle messages and conserves battery power until the next message is received. The simple matching operation consumes considerably less power than the full message processing typically carried out in conventional portable radios as described above.
If the compared messages do not match, the present invention further provides for voting plural copies of the subsequent message and then again comparing the voted message to the stored message to see if they match. Often, the failure to detect a match is simply the result of an erroneously received copy of the message. Many errors can be eliminated and a validly received message determined using a simple bit-by-bit voting algorithm of the plural copies of the received message. While the voting operation consumes some data processing overhead and therefore some added battery drain, it is significantly less than that required for CRC error detection/correction processing. Thus, if the voted message and the stored message match, the radio can avoid doing the CRC error detecting/checking data processing and thereby conserve power until the next message is received.
The present invention provides a battery-powered portable radio operable to monitor a particular radio channel for messages, e.g., a radio control channel, while still conserving power. In one embodiment, a programmable radio processor processes received messages by executing stored program instructions. At least one of the received messages is fully processed and stored in memory. A buffer is provided for storing received messages from the radio's transceiving circuitry. When the processor determines that a previously processed message stored by the processor is the same as a received message stored in the buffer, the processor discontinues further processing of that message to operate the radio in a battery conserving mode.
The buffer is part of a universal asynchronous receiver transmitter (UART) that buffers a predetermined number of digital words (bytes) corresponding to the length of an individual message frame. When that number of bytes is stored in the UART buffer, the UART sends an interrupt to the radio processor to wake the processor up out of its battery conserving mode. The processor then determines whether the buffered message matches the message previously stored by the processor. If there is a match, the radio is returned to the battery conserving mode of operation.
In another example embodiment of the present invention, application specific integrated logic circuity is specifically configured to perform (1) a voting operation for each received message copy in a message frame to generate a voted message and (2) a validity checking operation to check the validity of the voted message. Because the integrated logic is designed to specifically and efficiently perform these voting and validity checking operations using hardware circuitry, considerably less battery power is consumed relative to the power which would have been consumed if those same operations were performed using software programmed instructions executed by a programmable processor. In addition, the integrated logic circuity only sends to the programmable radio processor for further processing validly received messages which differ from a previously received message.